CdCl₂ Treatment-Induced Enhanced Conductivity in CdTe Solar Cells Observed Using Conductive Atomic Force Microscopy

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Understanding charge transport mechanisms in Cadmium Telluride (CdTe) photovoltaic devices is crucial for improving their efficiency.
• The role of grain boundaries and the impact of post-deposition treatments like Cadmium Chloride (CdCl2) on device performance require detailed investigation.

Purpose of the Study:

• To analyze the rear surfaces of CdTe photovoltaic devices without back contacts using conductive atomic force microscopy (C-AFM).
• To compare as-deposited and CdCl2-treated CdTe samples to understand the treatment's effect on charge flow.
• To clarify the influence of grains and grain boundaries on current transport under varying bias conditions.

Main Methods:

• Close-spaced sublimation (CSS) was used to grow CdTe photovoltaic devices.
• Conductive atomic force microscopy (C-AFM) was employed to map surface conductivity.
• Comparative analysis of as-deposited and CdCl2-treated CdTe samples under different electrical bias conditions.

Main Results:

• CdCl2-treated CdTe samples showed more homogeneous and enhanced current flow across grains compared to as-deposited samples.
• Grain boundaries exhibited variable current flow, dominating under specific reverse bias and breakdown conditions.
• Under opposite bias conditions, uniform current flow was observed with minimal contrast between grains and grain boundaries.

Conclusions:

• CdCl2 treatment improves CdTe crystallinity, leading to enhanced charge transport.
• Reduced p-type doping along grain boundaries after CdCl2 treatment is a key factor in improved performance.
• The study provides insights into charge transport mechanisms critical for optimizing CdTe solar cell design.